Conventionally, as display devices used in portable information terminals such as cellular phones, liquid crystal display devices making use of nematic liquid crystal have mainly been used, by virtue of their low drive voltage and low power consumption characteristics. In association with the recent rapid increase in the use of portable information terminals, the number of such liquid crystal display devices being produced has increased accordingly. At the same time, there has arisen demand for higher display performance, such as an increased number of pixels (characters).
In addition, in view of a desire to lengthen the period of time over which battery-based portable apparatus can be continuously operated, technologies that attain not only the aforementioned higher display functions, including higher resolution, but also lower electric power consumption are being pursued.
In one such pursuit, there have been proposed a variety of techniques involving use of a liquid crystal display device having a so-called display memory effect, which enables display to be maintained even after power supply to the liquid display device is cut.
By the employment of the memory effect, when no changes occur in the contents being displayed, in principle, power consumption can be reduced to zero. Also, power consumption can be reduced by applying voltage on a pixel-by-pixel basis to only those pixels that correspond to portions of the display to be changed.
Incidentally, as is well known in the art, when passive matrix drive is employed in conventional Twisted Nematic (TN) mode or Super-Twisted Nematic (STN) mode, an upper limit is imposed on the number of pixels which can be displayed, due to limitation imposed on the duty ratio. However, use of the memory effect eliminates the restriction imposed on the number of pixels.
Specific examples of conventional techniques which employ the aforementioned display memory effect include, among others, a technique in which ferroelectric liquid crystal is used [Applied Physics Letters, 36, 899 (1980); Japanese Patent Application Laid-Open (kokai) No. 107216/1981] and a technique in which nematic liquid crystal is combined with alignment layers which have undergone fine grating treatment (Japanese kohyo (PCT) Patent Publication No. 513809/1999).